1. Field of the Invention
This invention generally relates to the field of communication, and more particularly, to a system, method and computer-readable medium for actively cancelling interference signals in communication.
2. Description of the Prior Art
As a result of wireless communication being developed fast and becoming more popular, the interference in wireless communication systems is serious factor to decide system performance and efficiency. Therefore, how to cancel the interference in wireless systems turns out to be a development issue for the wireless communication equipment suppliers, carriers and the transceiver manufacturers.
Once, the wireless communication bandwidth was divided into several individual frequency channels for service vendors to dilute the problem of the system interference. With limited spectrum and fast growing demand for wireless communications, the wireless communication system, however, is sharing frequency channels for more service vendors. That is, one frequency channel has at least one communication system and each communication system modulates its own signal in different way to conduct communication process. Accordingly, the interference in the wireless communication channel is hard to avoid. The interference not only affects the radio coverage and system capacity but also reduces the transmission efficiency.
Referring to FIG. 1A, a transceiver T communicates in a wireless communication is illustrated. Base stations (or antenna sets) A, B, and C and a system S are distributed to form a network structure. The system S connects the base stations A, B, and C by wiring. The transceiver T communicates with the base station A via wireless transmission and there is no interference signal in the environment. Referring to FIG. 1B, the transmission coverage between a transceiver T and a base station A is depicted. The base station A serves wireless communication within a circle with solid line area, and the radio range of the transceiver T shows a circle with dot and line area. The intersection zone between the circle with solid line and the circle with dot and line is the communication area for the base station A to communicate with the transceiver T.
Referring to FIG. 1C, the communication between a transceiver T and a base station A affected by a base station B with the same communication system is shown. The transceiver T only communicates with the base station A through wireless communication, but the service area of the base station B with the same communication system overlaps the communication range between the transceiver T and the base station A. This leads to the transceiver T interfered by signals of the base station B, and such interference is called intra interference. Referring to FIG. 1D, the communication between a transceiver T and a base station A affected by a base station O with the different communication system is shown. The transceiver T only communicates with the base station A via wireless communication, but the service area of the base station O with the different communication system overlaps the communication range between the transceiver T and the base station A. This causes the transceiver T interfered by signals of the base station O, and such interference is called outer interference.
Referring to FIG. 1E, the communication between a transceiver T and a base station A affected by a base station B with the same communication system and base stations O and P with the different communication system is shown. The transceiver T only communicates with the base station A via wireless communication, although there are base stations B, O, and P in the same environment. Herein, the base station B has the same system to the base station A but the base stations O and P are different system from the base station A. FIG. 1E depicts a simple interference condition. That is, the communication between the transceiver T and the base station A is only affected by the interference signal of the base station B. The signals of the base stations O and P only affect the sending and receiving range of the transceiver T, but no affecting the communication between the transceiver T and the base station A.
Referring to FIG. 1F, the communication between a transceiver T and a base station A affected by a base station B with the same communication system and base stations O and P with the different communication system is shown. The transceiver T only communicates with the base station A via wireless communication, and there are other base stations B, O, and P existing in the same environment. Herein, the base station B is the same system to the base station A but the base stations O and P are different system from the base station A. As shown in FIG. 1F, there is interference between the communication of the transceiver T and the base station A. The interference includes the signals from the same system's base station B, and from the different system's base stations O and P.
With an extremely complex wireless communication environment, most of the wireless device vendors equip smart filters and decoders on their transceiver which filters and decodes its own signal from the physical channel. Yet the development of the transceivers trend to small and light and the communication circuit design is becoming more complex as well. Thus a revolution technology to mitigate and cancel interference in wireless communications is an essential development.
Recently, various schemes have been studied to suppress co-channel interference in co-working wireless networks. In M. H. M. Costa, “Writing on dirty paper”, IEEE Trans. Inf. Theory, vol. 49, no. 3. pp. 439-441, 1983., a frequency domain iterative multi-user detector for co-channel interference suppression in downlink of wireless cellular system was proposed. A zero forcing (ZF) scheme, which optimizes transmit and receive beamforming for multiuser MIMO to cancel the interference was considered in A. M. A. Ahmed, I. Marsland, “Co-channel interference cancellation in wireless cellular networks”, IEEE Vehicular Technology Conference, 2008. This work has been extended by combining with “dirty-paper” coding in Q. H. Spencer, A. L. Swindlehurst, and M. Haardt, “Zero-forcing methods for downlink spatial multiplexing in multiuser MIMO channels,” IEEE Tran. Signal Process, vol. 52, no. 2, pp. 461-471, 2004. The high complexity of dirty paper coding has made such a scheme difficult to be implemented in practical system. Furthermore, the algorithms require full channel state information (CSI) of all users at the transmitter, while each user only knows its own CSI in reality G. J. Foschini, K. Karakayali, and R. A. Valenzuela, “Coordinating multiple antenna cellular networks to achieve enormous spectral efficiency”, IEEE Proc. on Communications, vol. 153, no. 4, pp. 548-555, 2006. In IEEE Std 802.11., 2003 Edition, Std., a cooperative precoding and beamforming algorithm was proposed, which combines Tomlinson-Harashima precoding with transmit-receive beamforming based on W. Hardjawana, B. Vucetic, and Yonghui Li, “Cooperative Precoding and Beamforming in Co-working WLANs”, ICC'08 IEEE International Conference 2008, pp. 4759-4763. However, the drawbacks of all these schemes mentioned above are not only the complexity, but also some practical issues. One issue is that in all these schemes, the existing transmitter structure of base stations (BSs) and receiver structure of the mobile stations (MSs) have to be changed. This means that the manufactures have to redevelop the transceivers. This will increase the cost of system implementation and deployments. Nevertheless, such technology also incurs more energy consumption and it is not eco-friendly in the 21st century.
In view of the drawbacks mentioned with the prior art, there is a continuous need to develop a new and improved system, method and computer-readable medium that overcomes the disadvantages and shortages which are associated with the prior art. The advantages of the present invention are that it solves the problems mentioned above with more efficiency technology for wireless communication in the 21st century.